This invention relates to barrier-coated polyesters, preferably barrier coated polyethylene terephthalate (PET) and articles made therefrom. Preferably the barrier-coated PET takes the form of preforms having at least one layer of a barrier material and the bottles blow-molded therefrom. This invention further relates to methods of making articles formed of barrier coated polyester.
The use of plastic containers as a replacement for glass or metal containers in the packaging of beverages has become increasingly popular. The advantages of plastic packaging include lighter weight, decreased breakage as compared to glass, and potentially lower costs. The most common plastic used in making beverage containers today is PET. Virgin PET has been approved by the FDA for use in contact with foodstuffs. Containers made of PET are transparent, thin-walled, lightweight, and have the ability to maintain their shape by withstanding the force exerted on the walls of the container by pressurized contents, such as carbonated beverages. PET resins are also fairly inexpensive and easy to process.
Despite these advantages and its widespread use, there is a serious downside to the use of PET in thin-walled beverage containers: permeability to gases such as carbon dioxide and oxygen. These problems are of particular importance when the bottle is small. In a small bottle, the ratio of surface area to volume is large which allows for a large surface for the gas contained within to diffuse through the walls of the bottle. The permeability of PET bottles results in soft drinks that go xe2x80x9cflatxe2x80x9d due to the egress of carbon dioxide, as well as beverages that have their flavor spoiled due to the ingress of oxygen. Because of these problems, PET bottles are not suitable for all uses desired by industry, and for many of the existing uses, the shelf-life of liquids packaged in PET bottles is shorter than desired.
Although the plastic beverage container industry is large and competitive and the permeability problem with PET containers has been known since the inception of their use, there still is no good working solution to the permeability problem. Attempts to produce containers with barrier coatings have been heretofore largely unsuccessful.
Most of the problem with producing coated containers comes from the difficulty in finding suitable barrier materials. When most materials are placed on PET they will not adhere at all or they will adhere so weakly that they will delaminate from the PET over a short period of time or under minimal stress. Examples of such materials are polyvinylchloride (PVC) and polyvinylidene chloride (PVDC). Materials that do adhere to PET often do not have good barrier properties or have other characteristics that do not make them suitable for use in a low-cost commercial barrier coated container.
U.S. Pat. No. 5,464,106 to Slat, et al, describes bottles formed from the blow molding of preforms having a barrier layer. The barrier materials disclosed are polyethylene naphthalate, saran, ethylene vinyl alcohol copolymers or acrylonitrile copolymers. In Slat""s technique, the barrier material and the material to form the inner wall of the preform are coextruded in the shape of a tube. This tube is then cut into lengths corresponding to the length of the preform, and is then placed inside a mold wherein the outer layer of the preform is injected over the tube to form the finished preform. The preform may then be blow-molded to form a bottle. The drawbacks of this method are that most of the barrier materials disclosed do not adhere well to PET, and that the process itself is rather cumbersome.
A family of materials with good barrier characteristics are those disclosed in U.S. Pat. No. 4,578,295 to Jabarin. Such barrier materials include copolymers of terephthalic acid and isophthalic acid with ethylene glycol and at least one diol. This type of material is commercially available as B-010 from Mitsui Petrochemical Ind. Ltd. (Japan). These barrier materials are miscible with polyethylene terephthalate and form blends of 80-90% PET and 10-20% of the copolyester from which barrier containers are formed. The containers made from these blends are about 20-40% better gas barriers to CO2 transmission than PET alone. Although some have claimed that this polyester adheres to PET without delamination, the only preforms or containers disclosed were made with blends of these materials. There is no evidence that anyone heretofore has actually made a laminar preform or container using these materials from which to base such a statement.
Another group of materials, the polyamine-polyepoxides, have been proposed for use as a gas-barrier coating. These materials can be used to form a barrier coating on polypropylene or surface-treated PET, as described in U.S. Pat. No. 5,489,455 to Nugent, Jr. et al. These materials commonly come as a solvent or aqueous based thermosetting composition and are generally spray coated onto a container and then heat-cured to form the finished barrier coating. Being thermosets, these materials are not conducive to use as preform coatings, because once the coating has been cured, it can no longer be softened by heating and thus cannot be blow molded, as opposed to thermoplastic materials which can be softened at any time after application.
Another type of barrier-coating, that disclosed in U.S. Pat. No. 5,472,753 to Farha, relies upon the use of a copolyester to effect adherence between PET and the barrier material. Farha describes two types of laminates, a three-ply and a two-ply. In the three-ply laminate, an amorphous, thermoplastic copolyester is placed between the barrier layer of phenoxy-type thermoplastic and the layer of PET to serve as a tie layer to bind the inner and outer layers. In the two-ply laminate, the phenoxy-type thermoplastic is first blended with the amorphous, thermoplastic copolyester and this blend is then applied to the PET to form a barrier. These laminates are made either by extrusion or by injection molding wherein each layer is allowed to cool before the other layer of material is injected.
Thus, the need for barrier-coated PET preforms and containers which are economical, cosmetically appealing, easy to produce, and have good barrier and physical properties remains unfulfilled.
This invention relates to articles made of PET having coated upon the surfaces thereof one or more thin layers of thermoplastic material with good gas-barrier characteristics. The articles of the present invention are preferably in the form of preforms and containers. In preferred embodiments, the polyester comprises polyethylene terephthalate and the Phenoxy-type thermoplastic comprises a poly(hydroxyamino ether).
In one aspect, the present invention provides for a barrier-coated polyester article comprising at least one layer of amorphous polyester directly adhered to at least one layer of barrier material. The barrier material, which comprises a copolyester of terephthalic acid, isophthalic acid and at least one diol, has a glass transition temperature between 55 C. and 140 C., and has a permeability to oxygen and carbon dioxide which is less than that of polyethylene terephthalate.
In another aspect of the present invention there is provided a process for making a barrier-coated container comprising the steps of providing a barrier-coated polyester article in the form of a preform, such as that described above, and blow-molding the preform to the desired container shape.
In yet another aspect of the present invention there is provided a barrier coated preform comprising a polyester layer and a barrier layer comprising barrier material, wherein the polyester layer is thinner in the end cap than in the wall portion and the barrier layer is thicker in the end cap than in the wall portion.
In another aspect of the present invention, a multi-layer article comprising a wall portion comprising an inner multi-component layer and an outer layer. The inner multi-component layer has at least two discrete sublayers having an interface surface between the sublayers and extends longitudinally of the article, one of the sublayers comprising polyester and another of the sublayers comprising a barrier material comprising a (i) a Phenoxy-type Thermoplastic or (ii) a copolyester of terephthalic acid, isophthalic acid, and at least one diol, the barrier material having a permeability to carbon dioxide of no more than one-third of the permeability to carbon dioxide of polyethylene terephthalate. The outer layer comprises recycled polyester and the inner multi-component layer and the outer layer comprises materials with an absolute refractive index of 1.55-1.75.
In yet another aspect of the present invention there is provided a multi-layer preform comprising a wall portion having an inner layer and an outer layer. The inner layer comprises polyester, extends longitudinally of the preform terminating in a threaded neck finish section having externally upset threads to receive a closure member, has a support ring at the lower end of the threaded neck finish section, and has a thickness of at least two millimeters and an absolute refractive index of 1.55-1.65. The outer layer co-extends with the inner layer to terminate below the support ring and comprises (i) a copolyester of terephthalic acid, isophthalic acid, and at least one diol or (ii) a Phenoxy-type Thermoplastic selected from the group consisting of poly(hydroxy ether), poly(hydroxy ester ether), and poly(hydroxyamino ether), wherein the outer layer has a permeability to oxygen less than that of the inner layer and a thickness of no more than one-fourth the thickness of the inner layer. Additionally, the outer layer has an absolute refractive index of a value to provide a ratio of the refractive indices within the range of 1.0-1.2.
In a further aspect of the present invention there is provided a process for making a barrier coated polyester article comprising the steps of providing polyester article having at least one surface at a temperature of at least 100 C., and placing a barrier material on the heated surface of the polyester. The barrier material, comprising a Phenoxy-type Thermoplastic or a copolyester of terephthalic acid, isophthalic acid and at least one diol, has a glass transition temperature between about 55 C. and 140 C., and has a permeability to oxygen and carbon dioxide which is less than that of polyethylene terephthalate. In preferred embodiments, the coating process is done by dip coating, spray coating, flame spraying, electrostatic spraying, dipping the polyester article to be coated in a fluidized bed of barrier resin, or overmolding the polyester article with a melt of barrier material.
In another aspect of the present invention there is provided a method for making a barrier coated polyester article. A polyester article with at least an inner surface and an outer surface is formed by injecting molten polyester through a first gate into the space defined by a first mold half and a core mold half, where the first mold half and the core mold half are cooled by circulating fluid and the first mold half contacts the outer polyester surface and the core mold half contacts the inner polyester surface. Following this, the molten polyester is allowed to remain in contact with the mold halves until a skin forms on the inner and outer polyester surfaces which surrounds a core of molten polyester. The first mold half is then removed from the polyester article, and the skin on the outer polyester surface is softened by heat transfer from the core of molten polyester, while the inner polyester surface is cooled by continued contact with the core mold half. The polyester article, still on the core mold half is then placed into a second mold half, wherein the second mold half is cooled by circulating fluid. In the coating step, the barrier layer comprising barrier material is placed on the outer polyester surface by injecting molten barrier material through a second gate into the space defined by the second mold half and the outer polyester surface to form the barrier coated polyester article. The second mold half is then removed from the barrier coated article and then the barrier coated article is removed from the core mold half. The barrier materials used in the process preferably comprise a Phenoxy-type Thermoplastic or a copolyester of terephthalic acid, isophthalic acid and at least one diol.
In another aspect of the present invention, there is provided an xe2x80x9cinject-over-LIMxe2x80x9d process for the production of a multi-layer plastic container comprising several steps. A first polymer comprising a polyester and a second polymer comprising a copolyester of terephthalic acid, isophthalic acid and at least one diol are provided, and injected through a lamellar injection system to provide a composite multi-lamellae stream having at least one discrete lamella of polyester and at least another discrete lamella of the copolyester. The composite stream is then supplied to a mold to form an initial preform having inner and outer sublayers comprising polyester and the copolyester, wherein the sublayer comprising copolyester has a permeability to air which is less than the permeability to air of the sublayer comprising polyester. Recycled polyester is then supplied over the initial preform to form an outer layer to form a final preform. The final preform is then subjected to a blow molding operation to form a multi-layer plastic container.
In another aspect of the present invention there is provided a xe2x80x9cLIM-over-injectxe2x80x9d process for the production of a multi-layer plastic container. In this method, polyester is supplied to a mold to form an initial preform comprising polyester. A first body of a thermoplastic polymer comprising recycled polyester and a second body of thermoplastic barrier polymer comprising (i) a copolyester of terephthalic acid, isophthalic acid, and at least one diol or (ii) a Phenoxy-type Thermoplastic are provided and injected through a lamellar injection system having a coextrusion feed block unit to provide a composite multi-lamella stream having at least one discrete lamella of recycled polyester and at least one discrete lamella of the thermoplastic barrier polymer. The composite stream is supplied over the initial preform to form a final preform wherein the composite stream comprising sublayers of recycled polyester and the thermoplastic barrier material overlays the initial preform of polyester, and the final preform is subjected to a blow molding operation to form a multi-layer plastic container.
In a further aspect of the present invention, there is provided a method of making and coating preforms. The method begins by closing a mold comprising a stationary half and a movable half, wherein the stationary mold half comprises at least one preform molding cavity and at least one preform coating cavity and the movable mold half comprises a rotatable plate having mounted thereon a number of mandrels equal to the sum of the number of preform molding cavities and preform coating cavities. The remaining steps comprise: injecting a first material into the space defined by a mandrel and a preform molding cavity to form a preform having an inner surface and an outer surface; opening the mold; rotating the rotatable plate; closing the mold; injecting a second material into the space defined by the outer surface of the preform and the preform coating cavity to form a coated preform; opening the mold; removing the coated preform.
In further aspects of the above-described invention, the barrier materials of the present invention may further comprise Nanoparticles. The layer of barrier material in the articles of the present invention may consist of a plurality of microlayers comprising barrier material.